The 3GPP RAN LTE (Long Term Evolution) is currently studying transmission of SRSs (Sounding Reference Signals) for channel quality estimation (CQI (Channel Quality Indicator) estimation) for frequency scheduling, reception timing detection and transmission power control on uplink from a radio communication mobile station apparatus (hereinafter abbreviated as a “mobile station”) to a radio communication base station apparatus (hereinafter abbreviated as a “base station”) (e.g. see Non-Patent Document 1).
According to the 3GPP RAN LTE, for example, an SRS is formed with one LB (Long Block) and the time length of the SRS is 71.4 μs including the CP (Cyclic Prefix) and the reference signal. Furthermore, the mobile station transmits SRSs periodically (e.g. at 1-subframe intervals=at 1 ms intervals), according to command from the base station. Furthermore, a plurality of bandwidths, such as 1.25 MHz, 5 MHz and 10 MHz, are provided for the SRS transmission bandwidth, and a bandwidth corresponding to the propagation condition of the mobile station is set. For example, a mobile station located at a cell edge where the propagation condition is poor and transmission power is limited does not have power necessary to transmit a wideband SRS, and so the mobile station transmits a narrowband (e.g. 1.25 MHz) SRS. When such a narrowband SRS is used, wideband CQI estimation is performed over a plurality of transmission time fields by performing frequency hopping.
Furthermore, the 3GPP RAN LTE is studying the use of random access preamble (hereinafter abbreviated as a “preamble”) for initial access of a mobile station, updating of transmission timing and CQI estimation on uplink from a mobile station to a base station (e.g. see Non-Patent Document 2). A preamble is a signal including identification information about a mobile station, and each mobile station randomly selects one of a plurality of code sequences set up in advance by a base station or selects one code sequence according to command from the base station. Each mobile station then transmits a preamble generated based on the selected code sequence to the base station. According to the 3GPP RAN LTE, the preamble is formed with one subframe, for example, and the time length of the preamble is 1 ms (=14 LBs) including the CP, the preamble and the guard time, which is a non-transmission period. Furthermore, the mobile station transmits preambles periodically (e.g. at 10-subframe intervals=10 ms intervals), according to command from the base station as in the case of SRS. Furthermore, for the preamble transmission bandwidth, for example, 1.08 MHz is set (=6 RBs (Resource Blocks)). Furthermore, when the preamble is transmitted, frequency hopping is performed to provide frequency diversity gain and improve the preamble detection performance as in the case of the SRS.
Furthermore, a preamble transmitted from a mobile station which has not established synchronization with a base station on uplink entails a delay matching the round trip propagation delay time (RTD) at reception timing at the time of reception in the base station. Therefore, a guard time is set in the preamble as described above to prevent the preamble from delaying and causing interference with the signal of the next subframe.
When transmitting an SRS, resources of the time domain and frequency domain may be assigned thereto exclusive of other signals (e.g. see Non-Patent Document 3). Here, an SRS is assigned to the first 1 LB in one subframe (=1 ms) of PUSCH (Physical Uplink Shared Channel), which is formed with 14 LBs and assigned transmission data of the mobile station, and transmitted to the base station.
Non-Patent Document 1: NTT DoCoMo, Fujitsu, Mitsubishi Electric, NEC, Panasonic, Sharp, Toshiba Corporation, R1-072938, “Necessity of Multiple Bandwidths for Sounding Reference Signals”, 3GPP TSG RAN WG1 Meeting #49bis, Orlando, USA, Jun. 25-29, 2007
Non-Patent Document 2: Texas Instruments, R1-063213, “Improved Non-Synchronized Random Access structure for E-UTRA”, 3GPP TSG RAN WG1 Meeting #47bis, Riga, Latvia, Nov. 6-10, 2006
Non-Patent Document 3: NEC Group, NTT DoCoMo, R1-072824, “Discussion on Uplink Reference Signal”, 3GPP TSG RAN WG1 Meeting #49bis, Orlando, USA, 25-29 Jun. 2007